High-Speed Serial Interface Circuits and Systems

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Eustace Oliver Franklin
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1 High-Speed Serial Interface Circuits and Systems Design Exercise6 TX Drivers

2 Current-Mode Logic (CML) Driver Vdd Zo Zo TX P Zo RX P 2Zo Vinp TX N Vinn Zo RX N Vbias Current Steering Both sides are terminated by 50Ω Basic structure in high-performance serial link 2

Sources Output driver Specification 50Ω V_outp = V_outn = 200mV Vdiff_pk_pk = 400mV CML Driver Channel (mtline) Input MOSFET Length : 180n Width : 20u Source MOSFET Length : 1u Width : 750u

3 Sources Output driver Specification 50Ω V_outp = V_outn = 200mV Vdiff_pk_pk = 400mV CML Driver Channel (mtline) Input MOSFET Length : 180n Width : 20u Source MOSFET Length : 1u Width : 750u Vbias Voltage : 0.7 Input_source rand_bit_stream Tperiod : 1n Seed : 1 Vlogic _high : 1.8 Vlogic _low : 0 Vrise : 20p Vfall : 20p Mtline Type of Input : Tline Impedance : 50ohm Delay Time : 150p 3

4 CML Driver Simulation Results Rx_outp 200mV Rx_outn 400mV -200mV diff_out 4

5 Differential termination CML Driver Current Impedance matching with differential termination : 2Z O Vdd Vinp Zo Vbias ¼ Ⅰ Ⅰ Zo TX P ¾ Ⅰ TX N Vinn Zo Zo RX P 2Zo RX N V d + - V V V d _1 d _0 d _ pp V I R ( / 4)(2R) ( / 4)(2R) R d _ pp 5

6 Simulation Results (Current) Total current Termination current Total RMS current : 8.0 ma (V diff_pp 400mV condition) Termination RMS current : 2.0 ma (V diff_pp 400mV condition) 6

7 Simulation Results (Different Z 0 ) Reflection (time delay :300ps) Transmission Line : 50ohm Transmission Line : 75ohm 7

8 Replica Circuit for Output Swing Output swing voltage control Negative feedback Circuit Structure Alternative Circuit Structure AMP + - 2Vbias VDD-I D *R 1 Vout Vref Vbias 4 Vout Vdd 3 I D R I D 1Kohm VCVS circuit 이용 Gain : 1000 Max voltage : 1.8 Min voltage : 0 LPF 연결 V out+ V out- + _ V out+ V in+ V ss 1nF V in- V ref V dd VCVS V out+ - V out- = Gain * (V in+ - V in- ) Vbias 8

9 CML Driver w/ Replica Sources Replica Channel 9

Simulation Results for Different Swing V_diff_pp : 400mV (V ref = 1.8 0.

10 Simulation Results for Different Swing V_diff_pp : 400mV (V ref = V) Total RMS current : 16.0 ma V_diff_pp : 500mV (V ref = V) Total RMS current : 20.0 ma 10

11 Voltage-Mode (VM) Driver VDRV VZP M 1 D P M 2 M 4 TX P Zo RX P 2Zo D N M 3 M 5 TX N Zo RX N VZN M 6 11

12 VM Driver Schematic Output driver Specification 50Ω Vdiff_outp = 200mV Vdiff_pk_pk = 400mV Input MOSFET Length : 180n Width : 30u Current source MOSFET Length : 180n Width : 800u VZP bias Voltage : 935mV VZN bias Voltage : 495mV VDRV Voltage : 400mV 12

13 Simulation Results 300mV 100mV 200mV Rx_outp 200mV -200mV 400mV Rx_outn Diff_out 13

14 VM Driver Current Differential termination Impedance matching with differential termination : 2Z O V V V d_1 d_0 ( V / 2) V d _ pp s I V ( V / 2) d _ pp 4R s s 14

15 Simulation Results (Current) Total RMS current : 2.0 ma (V diff_pp 400mV condition) Termination RMS current : 2.0 ma (V diff_pp 400mV condition) Total current Termination current 15

16 Replica Circuit for VM Driver Circuit Structure VZP 3/4VDRV VDD 2Z O VDRV M1 Z O M2 Alternative Circuit Structure 3/4VDRV V in+ V out+ V in- V out- V ss 1Kohm 1nF + _ VDD VDRV VZP 2Z O M1 Z O M2 VDD 1/4VDRV VZN M4 Z O M6 1/4VDRV V in+ V in- V ss V out- + _ V out+ 1Kohm VDD 1nF VZN M4 Z O M6 16

17 Regulator Circuit for VM Driver Circuit Structure Alternative Circuit Structure VDD VDD VDD REF_VDRV REF_VDRV V in+ V out+ 1Kohm 1nF VDRV VMDRV Replica DRV V in- + _ V out- V ss VDRV VMDRV Replica DRV 17

18 VM Driver w/ Replica Replica for matching Regulator 18

19 Simulation Results for Different Swing V_diff_pp : 400mV Total RMS current : 4.0 ma V_diff_pp : 500mV Total RMS current : 5.0 ma 19

20 Simulation Results (Different Z 0 ) Reflection (time delay :300ps) Transmission Line : 50ohm Transmission Line : 75ohm 20

21 Power Consumption Comparison Current mode output driver RMS current : 16.0 ma (V diff_pp 400mV condition) Voltage mode output driver RMS current : 4.0 ma (V diff_pp 400mV condition) Current mode output driver Voltage mode output driver 21

22 Homework Current mode and voltage mode output driver Design V diff,p2p 600mV Current and voltage mode driver with 50ohm impedance. Derive mosfet size. Plot the output waveform and current waveform. Compare and analyze between current mode and voltage mode output driver. Plot the eye diagram in case of transmission line impedance 75ohm and 50ohm. (Differential Rx termination 50ohm condition) Plot the eye diagram in case of differential Rx termination 75ohm and 50ohm. (Transmission line impedance 50ohm condition) 22

High-Speed Serial Interface Circuits and Systems

High-Speed Serial Interface Circuits and Systems Design Exercise4 Charge Pump Charge Pump PLL ɸ ref up PFD CP LF VCO down ɸ out ɸ div Divider Converts PFD phase error pulse (digital) to charge (analog).